Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wako, 351-0198, Japan.
Department of Computer Science and Electronics, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka, 820-8502, Japan.
Sci Rep. 2017 May 24;7(1):2318. doi: 10.1038/s41598-017-02427-3.
Voltage or electric field induced magnetization dynamics promises low power spintronics devices. For successful operation of some spintronics devices such as magnetic oscillators and magnetization switching devices a clear understanding of nonlinear magnetization dynamics is required. Here, we report a detailed experimental and micromagnetic simulation study about the effect of excitation power on voltage induced local magnetization dynamics in an ultrathin CoFeB film. Experimental results show that the resonance line-width and frequency remains constant, whereas cone angle of the magnetization precession increases linearly with square-root of excitation power below threshold value, known as linear excitation regime. Above threshold power, the dynamics enters into nonlinear regime where resonance line-width monotonically increases and resonance frequency monotonically decreases with increasing excitation power. Simulation results reveal that a strong nonlinear and incoherent magnetization dynamics are observed in our experiment above the threshold power which reduces dynamic magnetic signal by suppressing large cone angle of magnetization precession. Moreover, a significant transfer of spin angular momentum from uniform FMR mode to its degenerate spin waves outside of excitation area further restrict the cone angle of precession within only few degrees in our device. Our results will be very useful to develop all-voltage-controlled spintronics devices.
电压或电场诱导的磁化动力学有望实现低功耗的自旋电子学器件。对于某些自旋电子学器件（如磁振荡器和磁化开关器件）的成功运行，需要清楚地了解非线性磁化动力学。在这里，我们报告了一项关于在超薄 CoFeB 薄膜中电压诱导局部磁化动力学的激励功率影响的详细实验和微磁模拟研究。实验结果表明，在阈值以下，共振线宽和频率保持不变，而磁化进动的圆锥角随激励功率的平方根线性增加，称为线性激励状态。在阈值功率以上，动力学进入非线性状态，其中共振线宽单调增加，共振频率随激励功率的增加而单调减小。模拟结果表明，在阈值功率以上，我们的实验中观察到了强烈的非线性和非相干的磁化动力学，这通过抑制大的磁化进动圆锥角来降低动态磁信号。此外，来自均匀 FMR 模式的自旋角动量向激励区域外的简并自旋波的显著转移进一步将进动圆锥角限制在我们器件中只有几度。我们的研究结果将对开发全电压控制的自旋电子学器件非常有用。
